San Juan weather in September

Averages from 2021–2025 (150 days of record).

Average high: 87°F
Average low: 78°F
Rainy days: ~20 per month
Total precipitation: 5.2 in
Warmest recorded: 93°F
Coldest recorded: 73°F

Expect September days in San Juan to top out around 87°F and cool to about 78°F overnight, with roughly 20 days of measurable rain across the month. In recent years September has ranged from 73°F to 93°F.

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Current San Juan forecast → · Historical data by Open-Meteo (ERA5).